As highlighted at a recent NIMH Research Roundtable, the field of psychiatry is in dire need of research addressing the special needs of children with severe mood and behavioral dysregulation who meet diagnostic criteria for bipolar disorder. Although studies have addressed clinical characteristics, family history, and treatment, no study to date has addressed the longitudinal course of children and adolescents with bipolar disorder. To help fill this gap and contribute important information about the validity of the diagnosis of pediatric-onset bipolar disorder, we propose a five-year follow-up study to assess the outcome of children and adolescents with DSM-IV bipolar disorder. At the completion of the current Mentored Clinical Scientist Development Award period, we will have ascertained 107 children and adolescents (73 children, 34 adolescents; 24 girls, 83 boys) with bipolar disorder along with 296 first-degree relatives. This sample has been well characterized along multiple domains of functioning (psychiatric, cognitive and psychosocial) as well as phenotypically (with photographs of face and hands) and genotypically (with blood samples of probands and first-degree relatives). Each proband and his or her parent(s) has been assessed in direct clinical interview by the Principal Investigator. At the follow-up assessment, we will examine the outcome of the probands and siblings in three domains of functioning: psychiatric, neuropsychological and psychosocial. Our intention is not only to determine which children with bipolar disorder continue to meet criteria or not, but to assess functioning in multiple domains over time. Our main aims regarding pediatric-onset bipolar disorder are to assess: 1) patterns of persistence and remission; 2) course; 3) patterns of comorbidity, neuropsychological functioning and psychosocial disability; 4) the course and outcome of high risk siblings; 5) the association with attention deficit hyperactivity disorder; 6) the association with conduct/antisocial disorder; 7) the association with substance use disorders; 8) the utility of the Child Behavior Checklist as a screening instrument. This follow-up study of children and adolescents with bipolar disorder seeks to contribute valuable information regarding the longitudinal course and outcome of pediatric-onset bipolar disorder in multiple domains.